1. Field of the Invention
The present invention relates a pressure-medium-operated clutch, especially for the drive train of a motor vehicle. Additionally, the invention also relates to a method for operating such a clutch.
2. Description of the Related Art
Pressure-medium-operated clutches can be used, for example, as drive components for an automatic-transmission-equipped motor vehicle, such as is described in German Patent DE 198 00 490. The automatic transmission can be a multiple-stage automatic transmission or it can be a continuously variable transmission (CVT), such as a belt-driven, conical pulley transmission. Such a clutch can also be utilized in a manually-operated transmission.
Pressure-medium-operated clutches have the disadvantage that, beginning at an unpressurized state, a comparatively long time elapses before torque is transmitted, because the clutch-activation cylinder must first be filled to cause engagement. During that time period critical vehicle or safety conditions can arise.
A purpose of the present invention is to provide a clutch and a method to activate the clutch in order to provide improved safety.
The present invention solves the problems by means having the advantageous features hereinafter described.
Briefly stated, in accordance with one aspect of the present invention, a pressure-medium-actuated clutch is provided that includes an annular pressure plate slidably supported for movement toward and away from a plurality of clutch disks. The pressure plate includes a piston surface that is spring biased toward a disengaged condition of the clutch. A pressure chamber is formed adjacent to and facing the piston surface, wherein the pressure chamber is adapted to receive pressurized fluid to cause the piston surface and pressure plate to move toward an engaged condition of the clutch. A pressure-medium control system includes at least one pilot-pressure-controlled valve, wherein at the beginning of actuation with a substantially unpressurized clutch pressure chamber the chamber is filled more quickly at higher pressure. A control means is provided that is operable upon reaching one of a desired pressure in the pressure chamber and a predetermined time interval to fill the pressure chamber with fluid more slowly.
In accordance with another aspect of the present invention a method is provided for operating a pressure-medium-operated clutch, the method including providing a pressure-reducing valve between a clutch pressure chamber and a source of pressurized fluid. A pilot pressure applied to a valve member carried within the pressure-reducing valve is controlled to provide a desired clutch-operating pressure.